A patent document 1 discloses a technique: determining that a vehicle is in a rapid deceleration state, in response to a condition that a change rate of a vehicle speed becomes greater than a predetermined determination value while the vehicle is decelerating; and stopping a fuel cut-off control of cutting off fuel supply to an internal combustion engine, in response to a condition that the fuel cut-off control is being implemented.
In a situation where the fuel cut-off control is implemented, torque of the internal combustion engine shifts from normal rotation into reverse rotation when the fuel cut-off control starts. This causes rotational fluctuation in a power train system, and thereby causes the vehicle to vibrate in a longitudinal direction thereof. The longitudinal vibration causes the change rate of the vehicle speed to fluctuate.
However, according to patent document 1, when the change rate of the vehicle speed becomes greater due to longitudinal vibration occurring at start of the fuel cut-off control, it may be determined incorrectly that the vehicle is rapidly decelerating although it is not decelerating rapidly in actuality, because the longitudinal vibration is not taken into account.